Chip Level Equalization for DS-CDMA Systems using Iterative Pilot Signals Enhancement

We present an iterative chip-level time domain equalizer (TEQ) for direct sequence code division multiple access (DS-CDMA) downlink with code multiplexed training symbols. For heavily loaded system, the multiple access interference (MAI) may be so severe that the pilot information offered by the training symbols are badly distorted. And this results in poorly converged equalizer coefficients. The proposed approach does not only utilize the training symbols, but also all the active and passive spreading codewords for TEQ adaptation. At each iteration, improved estimates of the transmitted data symbols are acquired and together with the pilot symbols, they are used to train the TEQ weights. Consequently, the signal-to-interference and noise (SINR) ratios of the effective training symbols is increased. Simulation results show that the proposed equalizer can achieve better bit-error rate performances than the generalized minimum mean squared error equalizer